The warship Fort Worth arrived in San Diego for the first time Thursday, but it already faces performance pressure.

The brand-new ship, third in the Navy’s littoral combat line, represents the lessons learned from two prototypes with records so rocky that critics have questioned the existence of this ground-breaking vessel, slated to make up a fifth of the U.S. fleet.

Since 2002, the U.S. Navy has envisioned its littoral class as the answer to enemies who lack equal navies but who are willing to make rogue attacks in shallow, coastal waters. San Diego will be home to as many as 16 of these ships by 2020.

The littoral warships are meant to be the fastest in the fleet, as nimble as a jet ski, and versatile, as they are basically a docking station waiting for specialized equipment to be plugged in for fighting mines, submarines or other surface ships.

But trouble started when the cost ballooned from $250 million to, finally, $537 million for the first ship and $653 million for the second, according to Navy figures. Since delivery, these two prototypes have suffered corrosion, mechanical breakdowns and cracks in the hull and elsewhere.

Congress has questioned the Navy, including in April demanding a report on the proposed 55-ship program.

So, expectations — and pressure — are mounting for the third ship, whose motto is “Grit and Tenacity.”

Arriving at the San Diego Naval Base pier Thursday morning, the Fort Worth looked much like its predecessor — the Freedom, Littoral Combat Ship (LCS) 1.

But naval and defense industry officials say there are significant changes under the hood.

The Fort Worth is about two yards longer in the stern, or back of the ship. Lead contractor Lockheed Martin said one of the results of the changes is improved buoyancy if the ship is damaged. The builder also increased the ship’s length underwater, which resulted in a few knots of additional speed, a 20 percent increase in fuel efficiency and the ability to carry an extra 10,000 gallons of fuel.

The ship’s skipper, Cmdr. Randy Blankenship, said the crew has noticed a comparative savings in fuel economy since the vessel left a Wisconsin shipyard this summer, but he couldn’t put a number on it.

The Freedom suffered cracks and fissures in the aluminum superstructure — the top of the ship that attaches to the steel deck. The Fort Worth’s superstructure is thicker to stave off that problem, said Timothy Fouts, a Lockheed senior manager for the LCS program.

The Freedom also suffered a crack in its hull. Fouts said the hull crack was caused by a bad weld. For the Fort Worth, which was still in the shipyard at the time, workers did quality checks to make sure there were no defects in later versions.

Since August, the Fort Worth has sailed down the Atlantic seaboard, through the Panama Canal and up the Pacific coast. In that short period, Blankenship said the crew has noticed no cracks.

Freedom experienced corrosion on the bottom of the hull and inside the ship’s rear bay, where the stern opens up to launch and retrieve small boats. For the Fort Worth, the builder added more strips that provide electrical current to counteract corrosion and increased the coverage area of anti-corrosion paint, among other things.

Some critics of the littoral program have been won over, at least in part.

Rep. Duncan Hunter, R-Alpine, who this year called the Navy onto the carpet for lacking “transparency” on this issue, declared his support after touring the second littoral ship, Independence, in August.

This week, Hunter’s press secretary said the House Armed Services Committee received a Sept. 20 classified presentation from the Navy on the littoral program. That also eased some of the congressman’s concern, but he continues to think the Navy shouldn’t put so many eggs in the LCS basket if it means shorting other ship classes, said spokesman Joe Kasper.

Criticism of fighting ability has heated up in recent weeks.

In a long piece on Time magazine’s Battleland blog this month, a retired Marine officer said the U.S. Navy’s littorals compare poorly with similar-sized foreign warships on firepower, for the price.

The Navy shot back in an Oct. 10 statement by Rear Adm. John Kirby, the Navy’s chief of information.

Kirby said naval officials are “more than comfortable” that the ships can fight and defend themselves in combat. He also said later littoral ships will come in below $460 million, though the Navy has declined to issue an exact figure.

The Fort Worth’s big gun is the BAE 57 mm, mounted on the front deck. The crew didn’t want to name its maximum range, but industry literature pegs it at 10 miles. It is joined by the ship’s rolling airframe missiles, intended to shoot down incoming projectiles. The ship also carries a “chaff” system, which spews decoys to confuse inbound missiles.

Those weapons are all meant for self-defense. To go on offense, the ship would lean on whatever it receives in the eventual anti-ship mission package.

The Navy is still working out the details, but it will likely include two 30mm MK-46 guns and possibly a Griffin missile system.

Questions about survivability also arose in a 2011 report by the Pentagon’s director of operational test and evaluation that said the littorals are “not expected to be survivable in a hostile combat environment.”

The Fort Worth’s current skipper — who started his career as an enlisted boatswain’s mate and served on an aircraft carrier, destroyers and cruisers — said he likes his small ship’s chances in a fight.

“If I was going into combat, what am I going into combat for? It’s not to fight another destroyer. I’m going after pirates, and swarm tactics” by small enemy boats, said Blankenship, 44.

“We have a limited set of resources in this country, and we have a responsibility to live within our means. So we look at the littoral threat, which is where most of the issues in the world are these days. I’m not going up against big ships. I’m going up against little ships,” he said. “So absolutely this is the right platform and right expense for us.”

Vice Adm. Tom Copeman, commander of naval surface forces in San Diego, met the Fort Worth as it arrived Thursday. He sits on a four-admiral panel announced in August to keep a sharp eye on the LCS program.

In February, the Fort Worth will go through the final trials before the Navy accepts full responsibility for its performance. The Navy will take notes from those and from the first deployment of the Freedom, slated to spend eight months in Singapore early next year.

One of the things under the microscope, according to Copeman: crew size. At present, the Navy has a 40-person core crew running what is an almost 400-foot-long ship.

“We will take lessons learned from that. We don’t rule anything out, and we try to be flexible,” Copeman said, standing on the Fort Worth’s flight deck Thursday morning.

“We’ve got to get it right.”

LCS timeline

Key dates in the development of the Navy’s littoral combat ships:

Nov. 1, 2001: Navy initiates program to create a fleet of new warships designed for coastal warfare.

June 2, 2005: Keel laid for first LCS 1 Freedom at the Marinette Marine shipyard in Wisconsin. The Lockheed Martin-designed Freedom was christened and launched in September 2006 and was commissioned Nov. 8, 2008.

January 2006: Keel laid for the General Dynamics-designed LCS 2 Independence at the Austal USA shipyard in Mobile, Ala. Ship was launched in April 2008 and commissioned Jan. 16, 2010.

2007: The Navy scrubs two of four prototypes because costs had more than doubled.

Sept. 16, 2009: Navy announces a single contractor would be chosen.

April 23, 2010: Freedom arrives in San Diego. In May, the ship develops problems with a water jet that had to be repaired.

Dec. 29, 2010: Navy awards two companies contracts that could be worth a total of more than $7 billion, saying it was splitting the purchase to obtain the vessels more quickly.

2011: After a hull crack is discovered during sea trials, the Freedom enters dry-dock at BAE Systems San Diego Ship Repair in June.

Feb. 1, 2012: A shaft seal leak causes minor flooding while the Freedom is at sea.

May 2, 2012: Independence sails into San Diego Bay.

Oct 18, 2012: Fort Worth arrives in San Diego

SOURCES: Congressional Research Service, Government Accountability Office and news service reports.